I have plenty of hols to book this year at work at the mo, so should be able to get a good few days off while you're down to do some local cruising with you.
Provided the weather is in our favour, trips out round Skomer, out to Grassholm, and up the coast can definately be in order. Going down to Tenby is only really going to be great when the range is closed on the weekend or we have to go a long way from land to be out of the exclusion zone, which means you won't be seeing much wildlife apart from that unusual bird, the seagul
There are good high tides that week you're down - low tide plonk right in the middle of the day tho, which will rule out going right up river to explore the out of the way places unfortunately.
So far this year, I have ventured out to Skomer, and then past, round the coast to Broad Haven. Both on pretty good days, and were thoroughly enjoyable with lots of wildlife around, and cracking scenery.
When you know for definate dates etc... let me know and I will book some leave.